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Three-Dimensional Convection in an Inclined Porous Layer Subjected to a Vertical Temperature Gradient

Fluid Dynamics & Materials Processing 2024年第9期20卷 1957-1970页

作者： Ivan Shubenkov Tatyana Lyubimova Evgeny Sadilov Computational Fluid Dynamics laboratory Institute of Continuous Media Mechanics UB RASPerm614068Russia Theoretical Physics Department Perm State UniversityPerm614990Russia

In this paper,we study the onset and development of three-dimensional convection in a tilted porous layer saturated with a *** layer is subjected to a gravitational field and a strictly vertical temperature ***,problems of thermal convection in tilted porous media saturated with a liquid are studied by assuming constant different temperatures at the boundaries of the layer,which prevent these systems from supporting conductive(non-convective)*** boundary conditions considered in the present work allow a conductive state and are representative of typical geological *** an earlier work,we carried out a linear stability analysis of the conductive *** was shown that at any layer tilt angles,the most dangerous type of disturbances are longitudinal ***,a non-zero velocity component exists in *** the present work,threedimensional non-linear convection regimes are *** original three-dimensional problem is reduced to two-dimensional one with an analytical expression for the velocity z-component v_(z)=v_(z)(x,y).It is shown that the critical Rayleigh number values obtained through numerical solutions of the obtained 2D problem by a finite difference method for different layer inclination angles,are in a good agreement with those predicted by the linear *** number of convective rolls realized in nonlinear calculations also fits the linear theory predictions for a given cavity *** carried out at low supercriticalities show that a direct bifurcation takes *** increasing supercriticality,no transitions to other convective regimes are *** situation studied in this problem can be observed in oil-bearing rock formations under the influence of a geothermal temperature gradient,where the ensuing fluid convection can affect the distribution of oil throughout the layer.

关键词： Thermal convection inclined layer porous media vertical temperature gradient

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Integration of bio-inspired limb-like structure damping into motor suspension of high-speed trains to enhance bogie hunting stability

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Railway Engineering Science 2024年第3期32卷 324-343页

作者： Heng Zhang Liang Ling Sebastian Stichel Wanming Zhai State Key laboratory of Rail Transit Vehicle System Southwest Jiaotong UniversityChengdu 610031China Department of Engineering mechanics KTH Royal Institute of TechnologyStockholmSweden

Hunting stability is an important performance criterion in railway *** study proposes an incorporation of a bio-inspired limb-like structure(LLS)-based nonlinear damping into the motor suspension system for traction units to improve the nonlinear critical speed and hunting stability of high-speed trains(HSTs).Initially,a vibration transmission analysis is conducted on a HST vehicle and a metro vehicle that suffered from hunting motion to explore the effect of different motor suspension systems from on-track ***,a simplified lateral dynamics model of an HST bogie is established to investigate the influence of the motor suspension on the bogie hunting *** bifurcation analysis is applied to optimize the motor suspension parameters for high critical ***,the nonlinear damping of the bio-inspired LLS,which has a positive correlation with the relative displacement,can further improve the modal damping of hunting motion and nonlinear critical speed compared with the linear motor suspension ***,a comprehensive numerical model of a high-speed train,considering all nonlinearities,is established to investigate the influence of different types of motor *** simulation results are well consistent with the theoretical *** benefits of employing nonlinear damping of the bio-inspired LLS into the motor suspension of HSTs to enhance bogie hunting stability are thoroughly validated.

关键词： High-speed train Hunting stability Bio-inspired limb-like structure Motor suspension nonlinear damping

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稀薄气体效应对高超声速边界层稳定性的影响

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Acta Mechanica Sinica 2024年第3期40卷 10-27页

作者：欧吉辉王晨悦陈杰 laboratory of High-speed Aerodynamics Tianjin UniversityTianjin300072China Department of mechanics Tianjin UniversityTianjin300072China Tianjin Key laboratory of Modern Engineering mechanics Tianjin300072China

临近空间高超声速飞行器在跨越大气层飞行时可能经历从连续到稀薄流域.本文基于Navier-Stokes(NS)方程和NS改进模型研究了稀薄气体效应对高超声速边界层稳定性的影响.首先在传统线性稳定性理论(linear stability theory,LST)中引入壁面... 详细信息

临近空间高超声速飞行器在跨越大气层飞行时可能经历从连续到稀薄流域.本文基于Navier-Stokes(NS)方程和NS改进模型研究了稀薄气体效应对高超声速边界层稳定性的影响.首先在传统线性稳定性理论(linear stability theory,LST)中引入壁面滑移条件和非线性输运模型,发展了适用于稀薄剪切流的拓展稳定性分析方法.然后重点分析了马赫数10、飞行高度55 km的尖平板绕流,研究了稀薄气体效应(包括壁面滑移效应和剪切非平衡效应)对边界层稳定性的影响机理.结果表明,对于基本流,稀薄气体效应使得边界层变薄,边界层剖面的广义拐点向壁面靠近.对于稳定性,稀薄气体效应通过影响基本流使第二模态更稳定,而通过修正稳定性方程使第二模态更不稳定,综合效应使得第二模态更稳定.然而,对于第一模态,稀薄气体效应始终起不稳定效果.这些结果从宏观角度揭示了近连续流域高超声速平板边界层的稳定性特征.

关键词： Linear instability Flat-plate boundary layer Rarefied nonequilibrium Hypersonic Slip effects

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Matched Volterra reduced-order model for an airfoil undergoing periodic translation

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Chinese Journal of Aeronautics 2024年第1期37卷 19-23页

作者： Lianrui NIE Ziniu WU Department of Engineering mechanics Tsinghua UniversityBeijing 100084China

This paper is devoted to application of the Reduced-Order Model(ROM)based on Volterra series to prediction of lift and drag forces due to airfoil periodic translation in transonic flow *** there is large amplitude oscillation of the relative Mach number,as appeared in helicopter rotor movement in forward flight,the conventional Volterra ROM is found to be *** cover such applications,a matched Volterra ROM,inspired from previous multistep nonlinear indicial response method based on Duhamel integration,is thus considered,in which the step motions are defined inside a number of equal intervals with both positive and negative step motions to match the airfoil forward and backward movement,and the kernel functions are constructed independently at each *** shows that,at least for the translation movement considered,this matched Volterra ROM greatly improves the accuracy of ***,the matched Volterra ROM,with the total number of step motions and thus the computational cost close to those of the conventional Volterra ROM method,has the additional advantage that the same set of kernels can match various translation motions with different starting conditions so the kernels can be predesigned without knowing the specific motion of airfoil.

关键词： Airfoil periodic translation Lift and drag Reduced-order model Transonic flow Unsteady flow

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磁性软材料的光热编程实现复杂且可重构的三维形变（英文）

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Science China Materials 2024年

作者：鲍义文李霁雨汪韬王柳徐航勋 Collaborative Innovation Center of Chemistry for Energy Materials (iChEM) Key Laboratory of Precision and Intelligent Chemistry Department of Polymer Science and Engineering University of Science and Technology of China CAS Key laboratory of Mechanical Behavior and Design of Materials Department of Modern Mechanics University of Science and Technology of China State Key laboratory of nonlinear mechanics Institute of Mechanics Chinese Academy of Sciences

响应性软材料能够在外部刺激下进行复杂、可逆且快速的几何变形,在微创医学、可穿戴设备和软体机器人等领域具有巨大应用潜力.在本研究中,我们提出了一种通过光热编程设计可重构三维变形磁性软材料的新方法.通过将硬磁性颗粒嵌入由纤维...

响应性软材料能够在外部刺激下进行复杂、可逆且快速的几何变形,在微创医学、可穿戴设备和软体机器人等领域具有巨大应用潜力.在本研究中,我们提出了一种通过光热编程设计可重构三维变形磁性软材料的新方法.通过将硬磁性颗粒嵌入由纤维状聚吡咯(PPy)和半结晶聚合物组成的聚合物材料中,我们开发出了一种磁性复合材料,该材料可以在外部磁场下进行远程控制,实现精确的可编程变形.该方法重要的创新点在于,利用PPy的光热效应,当材料受到红外光辐照时,复合材料的黏度发生暂时改变,从而允许磁性颗粒进行动态可控定向运动;冷却后,磁性各向异性固化,材料能够快速且可逆地进行几何变形.该方法能够对磁化分布进行精细控制,从而开发出多功能设备,具有诸如软体机器人复杂三维变形、多模态电气开关、可重写的快速响应码以及可变形夹具等多种潜在应用.本研究不仅加深了对软材料中磁矩编程的理解,也为自适应和响应性材料的设计开辟了新的途径,推动了先进技术应用的发展.

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nonlinear dynamics of a circular curved cantilevered pipe conveying pulsating fluid based on the geometrically exact model

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Applied Mathematics and mechanics(English Edition) 2024年第2期45卷 261-276页

作者： Runqing CAO Zilong GUO Wei CHEN Huliang DAI Lin WANG Department of Engineering mechanics School of Aerospace EngineeringHuazhong University of Science and TechnologyWuhan 430074China Hubei Key laboratory for Engineering Structural Analysis and Safety Assessment Wuhan 430074China State Key laboratory of Intelligent Manufacturing Equipment and Technology School of Mechanical Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074China

Due to the novel applications of flexible pipes conveying fluid in the field of soft robotics and biomedicine,the investigations on the mechanical responses of the pipes have attracted considerable *** fluid-structure interaction(FSI)between the pipe with a curved shape and the time-varying internal fluid flow brings a great challenge to the revelation of the dynamical behaviors of flexible pipes,especially when the pipe is highly flexible and usually undergoes large *** this work,the geometrically exact model(GEM)for a curved cantilevered pipe conveying pulsating fluid is developed based on the extended Hamilton's *** stability of the curved pipe with three different subtended angles is examined with the consideration of steady fluid *** attention is concentrated on the large-deformation resonance of circular pipes conveying pulsating fluid,which is often encountered in practical *** constructing bifurcation diagrams,oscillating shapes,phase portraits,time traces,and Poincarémaps,the dynamic responses of the curved pipe under various system parameters are *** mean flow velocity of the pulsating fluid is chosen to be either subcritical or *** numerical results show that the curved pipe conveying pulsating fluid can exhibit rich dynamical behaviors,including periodic and quasi-periodic *** is also found that the preferred instability type of a cantilevered curved pipe conveying steady fluid is mainly in the flutter of the second *** a moderate value of the mass ratio,however,a third-mode flutter may occur,which is quite different from that of a straight pipe system.

关键词： curved pipe conveying fluid pulsating fluid geometrically exact model(GEM) nonlinear dynamics parametric vibration flutter

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Inverse design of mechanical metamaterial achieving a prescribedconstitutive curve

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Theoretical & Applied mechanics Letters 2024年第1期14卷 16-22页

作者： Zongliang Du Tanghuai Bian Xiaoqiang Ren Yibo Jia Shan Tang Tianchen Cui Xu Guo State Key laboratory of Structural Analysis Optimization and CAE Software for Industrial EquipmentDepartment of Engineering MechanicsDalian University of TechnologyDalian 116023China Ningbo Institute of Dalian University of Technology Ningbo 315016China

Besides exhibiting excellent capabilities such as energy absorption,phase-transforming metamaterials offer a vast design space for achieving nonlinear constitutive *** is facilitated by switching between different patterns under ***,the related inverse design problem is quite challenging,due to the lack of appropriate mathematical formulation and the convergence issue in the post-buckling analysis of intermediate *** this work,periodic unit cells are explicitly described by the moving morphable voids method and effectively analyzed by eliminating the degrees of freedom in void ***,by exploring the Pareto frontiers between error and cost,an inverse design formulation is proposed for unit *** formulation aims to achieve a prescribed constitutive curve and is validated through numerical examples and experimental *** design approach presented here can be extended to the inverse design of other types of mechanical metamaterials with prescribed nonlinear effective properties.

关键词： Metamaterial Pattern-transformation Constitutive curve Inverse design

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Optical third-harmonic generation of spherical quantum dots under inversely quadratic Hellmann plus inversely quadratic potential

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Communications in Theoretical Physics 2024年第9期76卷 160-165页

作者： Xing Wang Xuechao Li School of mechanics and Photoelectric Physics Anhui University of Science and Technology

The third-harmonic generation（THG） coefficient for a spherical quantum dot system with inversely quadratic Hellmann plus inversely quadratic potential is investigated theoretically,considering the regulation of quantum size, confinement potential depth and the external environment. The numerical simulation results indicate that the THG coefficient can reach the order of 10-12m2V-2, which strongly relies on the tunable factor, with its resonant peak experiencing a redshift or blueshift. Interestingly, the effect of temperature on the THG coefficient in terms of peak location and size is consistent with the quantum dot radius but contrasts with the hydrostatic pressure. Thus, it is crucial to focus on the influence of internal and external parameters on nonlinear optical effects, and to implement the theory in practical experiments and the manufacture of optoelectronic devices.

关键词： inversely quadratic hellmann potential inversely quadratic potential nonlinear optical effects quantum dot third harmonic generation coefficient

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Anisotropic time-dependent behaviors of shale under direct shearing and associated empirical creep models

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Journal of Rock mechanics and Geotechnical Engineering 2024年第4期16卷 1262-1279页

作者： Yachen Xie Michael Z.Hou Hejuan Liu Cunbao Li Shenzhen Key laboratory of Deep Engineering Sciences and Green Energy Shenzhen UniversityShenzhen518060China Institute of Subsurface Energy Systems Clausthal University of TechnologyClausthal-Zellerfeld38678Germany State Key laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China

Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging *** this context,we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e.0°,30°,45°,60°,and 90°),under multiple levels of direct shearing for the first *** results show that the anisotropic creep of shale exhibits a significant stress-dependent *** a low shear stress,the creep compliance of shale increases linearly with the logarithm of time at all bedding orientations,and the increase depends on the bedding orientation and creep *** high shear stress conditions,the creep compliance of shale is minimal when the bedding orientation is 0°,and the steady-creep rate of shale increases significantly with increasing bedding orientations of 30°,45°,60°,and 90°.The stress-strain values corresponding to the inception of the accelerated creep stage show an increasing and then decreasing trend with the bedding orientation.A semilogarithmic model that could reflect the stress dependence of the steady-creep rate while considering the hardening and damage process is *** model minimizes the deviation of the calculated steady-state creep rate from the observed value and reveals the behavior of the bedding orientation's influence on the steady-creep *** applicability of the five classical empirical creep models is quantitatively *** shows that the logarithmic model can well explain the experimental creep strain and creep rate,and it can accurately predict long-term shear creep *** on an improved logarithmic model,the variations in creep parameters with shear stress and bedding orientations are *** abovementioned findings,a mathematical method for constructing an anisotropic shear creep model of shale is proposed,which can characterize the nonlinear dependence of the anisotropic shear creep behavior of shale on the bedding orientation.

关键词： Rock anisotropy Direct shear creep Creep compliance Steady-creep rate Empirical model Creep constitutive model

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Enhanced wide-angle third-harmonic generation in flat-band-engineered quasi-BIC metagratings

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Science China(Physics,mechanics & Astronomy) 2024年第4期67卷 81-87页

作者： Yijia Zang Ruoheng Chai Wenwei Liu Zhancheng Li Hua Cheng Jianguo Tian Shuqi Chen The Key laboratory of Weak Light nonlinear Photonics Ministry of EducationSchool of Physics and TEDA Institute of Applied PhysicsNankai UniversityTianjin 300071China School of Materials Science and Engineering Smart Sensing Interdisciplinary Science CenterNankai UniversityTianjin 300350China The Collaborative Innovation Center of Extreme Optics Shanxi UniversityTaiyuan 030006China

nonlinear metasurfaces and photonic crystals provide a significant way to generate and manipulate nonlinear signals owing to the resonance-and symmetry-based light-matter interactions supported by the artificial ***,the nonlinear conversion efficiency is generally limited by the angular dispersion of optical resonances especially in nonparaxial ***,we propose a metagrating realizing a quasi-bound-state in the continuum in a flat band to dramatically improve the third harmonic generation(THG)efficiency.A superior operating angular range is achieved based on the interlayer and intralayer couplings,which are introduced by breaking the mirror symmetry of the *** demonstrate the relation of angular dispersion between the nonlinear and linear responses at different incident *** also elucidate the mechanism of these offaxis flat-band-based nonlinear conversions through different mode *** scheme provides a robust and analytical way for nonparaxial nonlinear generation and paves the way for further applications such as wide-angle nonlinear information transmission and enhanced nonlinear generation under tight focusing.

关键词： nonlinear metasurfaces quasi-bound-state in the continuum angular dispersion third harmonic generation efficiency

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